Field of Invention
The present invention is generally related to a pedal assembly of a vehicle, and, more particularly, variable ratio actuating assemblies for vehicles, such as brake pedal assemblies having a variable pedal ratio.
Description of Related Art
A pedal, such as a brake pedal, is mounted to a dash panel in a vehicle so as to provide a driver easy access and manipulation via his/her foot. For example, known brake pedal assemblies include a pedal arm having one end that is pivotally mounted to a mounting structure (e.g., a bracket) provided in the vehicle to enable pivotal movement of the pedal arm about an operating pivot axis. The pedal arm includes an input connector in the form of a booster pin. This booster pin operatively connects to a master cylinder or brake booster push rod that is configured to actuate the master cylinder of the vehicle brake system for purposes of selectively engaging or disengaging the vehicle's brakes. The booster pin is positioned between the operating pivot axis of the pedal arm and a pedal foot pad at an end of the pedal arm opposite the end of the operating pivot axis.
The feel and effectiveness of the braking action experienced by the operator can be varied by changing the geometric pedal ratio, which refers to the geometric relationship between the levers and pivot points that make up the brake pedal assembly. This geometric ratio is related to the pedal's force ratio FB/FA, where FA is the amount of force applied to the input portion (e.g., the pedal pad) and FB is the amount of force applied to the input element (e.g., the brake booster rod). The geometric pedal ratio for a fixed relationship between levers is typically expressed as R=a/b, where a is the distance between the operating pivot axis and the actuation point on the pedal foot pad, and b is the distance between the operating pivot axis and the master cylinder push rod attachment point, i.e., the booster pin. In general, for a given pedal arm travel at a given input force, pedal assemblies with higher geometric pedal ratios generate greater forces that are applied to the brake system. However, the higher pedal ratio results in a shorter travel of the master cylinder push rod. Additionally, the higher pedal ratio affects the “pedal feel” in the braking action to the user, thus altering the operator's perception of comfort or reasonable operation.
Variable ratio brake pedal assemblies are known in the art. For example, see U.S. Patent Application Publication No. 2003/0106392 and U.S. Pat. Nos. 4,615,235 and 7,219,576. However, these variable ratio brake pedal assemblies include complex linkage mechanisms. Mechanisms with long linkages tend to give a continuously increasing curve for variable ratio, which is not desirable as the driver can experience push back while the brake is released. Prior designs also have a high degree of movement (e.g., up to 40 mm). Mechanisms with shorter linkages may provide better performance curves, but they tend to interfere with packaging of the pedal mechanism/foot controls below the instrumental panel, particularly when users with large shoes or work boots are activating the controls. Mechanisms with cam designs are prone to wear and noise performance issues.